John randomly started getting the message that said "No SIM Card" on his iPad 2. He took it to AT&T and they gave him a new SIM card, but after a couple weeks, it started giving him that message again. Leo suspects the issue is something in the iPad, such as a short circuit that's actually frying SIM cards. It is an older iPad, and Leo suggests bringing it to the Apple store. But it most likely won't be a free repair. He shouldn't do anything to it himself -- he should have Apple look at it.
It might just be time to get a new one, though.